There are various passive vehicle seat belt systems in which an occupant restraint belt leads outwardly from a retractor affixed adjacent the lower rear of the inboard side of the seat to an anchor located on the outboard side of the seat. An anchor may, in the case of shoulder belts, be a fixed anchor fastened to the upper rear corner of the vehicle door, in which case the belt shifts forward away from the occupant to a releasing position when the door is opened. A fixed anchor may also be attached to the vehicle body above and behind the occupant's shoulder, and a mechanically or electrically drive transfer guide ring is moved along a track affixed at the edge of the roof above the door between a restraint location near the anchor and a release location near or along the front pillar of the vehicle. Instead of a fixed anchor and a transfer ring, the outboard end of a shoulder belt can be connected to a movable anchor carried by a track above the vehicle door. In the case of a lap belt, the outboard end of the belt is attached to a fixed anchor on the lower rear portion of the door and a portion of the belt is transferred by a guide ring that moves along a track of the door. Alternatively, the lap belt may be transferred between a restraining location near the lower rear corner of the door to a releasing location near the front of the door by a mechanically or electrically driven moving anchor. Various specific designs of all of the above arrangements are known in the prior art.
Many systems of the types described above present problems during assembly of the vehicle when it is being manufactured on the conventional vehicle assembly line, inasmuch as it is often necessary for the guide rails and other components of the restraint system to be installed before the inner panels and coverings on the roof or door are installed. If the belt is already partly or fully assembled to the guides and anchors, it can interfere with the installation of linings and coverings as well as with other assembly procedures within the passenger compartment.
Some specific belt systems have a buckle for connecting the outboard end of the belt to the vehicle door or body. Such a buckle allows the installation of anchors, guide rails and other components of the system while the belt remains unattached to the outboard part of the vehicle and wound conveniently out of the way on the retractor. The buckle also serves as an emergency release device that is accessible from outside the vehicle and can be disconnected by someone coming to the assistance of an injured or trapped occupant in case the occupant is to be removed from the vehicle and, for one reason or another, the normal function of the passive belt system is prevented. Of course, the occupant may also have to release himself from the belt in some situations.
Despite the advantages of a buckle for connecting the outboard end of a lap or shoulder belt to a fixed or moving anchor, such a buckle has the disadvantage of being subject to being released by an occupant who does not wish to wear the belt, even though an important reason for having a passive belt system in a vehicle is to encourage an occupant to wear the belt by eliminating the inconvenience of connecting and disconnecting it. Moreover, a child might disconnect the belt and be endangered, and the driver may not be able to reconnect the belt or if he tries to do so, will be distracted from operating the vehicle. Ordinarily the buckle is attached to the anchor and the buckle tongue is on the belt, and the buckle, because it is of comparatively large size, can be a hazard to the occupant. In the case of moving anchors, the buckle increases the weight and therefore the driving force required to move the anchor between the releasing and restraining locations.